Introduction to reactive programming. Jonas Chapuis, Ph.D.

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1 Introduction to reactive programming Jonas Chapuis, Ph.D.

2 Reactive programming is an asynchronous programming paradigm oriented around data flows and the propagation of change wikipedia

3 Things happening at arbitrary times Movements and transformations of data Evolution of the state of the world asynchronous change data flows

4 asynchronous data flows flowsof change

5 Modern requirements 10 years ago now Server nodes 10 s 1000 s Response times seconds milliseconds Service availability 95% % Data volumes GBs TBs & PBs

Netflix: the reactive company Founded in 1997, streaming since 2007 94 million subscribers, 9 billion US$ 35.

6 Netflix: the reactive company Founded in 1997, streaming since million subscribers, 9 billion US$ 35.2% downstream traffic in the US +5 billion API requests per day Reactive and asynchronous from front to back (RxJava, RxJS, Redux-Observable) Microservices resilience & monitoring: Hystrix

7 Source: Golden age of APIs

8 Source: Golden age of APIs

9 Microservices

10 Source: Microservices

11 Reactive Manifesto Responsive Elastic Resilient Message Driven Source: The Reactive Manifesto

12 Messages Occurrence of an event (e.g. mouse click, door opened, etc.) Request or response State of a (sub)system In fact, any piece of information

13 Message-driven: availability of new information drives the system (vs control flow driven by a thread-of-execution)

14 Example: time to leave feature in Cortana Higher-order query operators userlocation.sample(1 * M).DistinctUntilChanged().Select(here => Device-side event stream Cloud-side event stream traffic(here, meetinglocation).select(t => meeting t.estimatedtime)).switch().select(t => Leave now for GVA + t)

15 Push versus Pull Anything new going on, Alice? - No, same old Erik Anything new on your side, Carol? - Oh yes you've just missed all the action Alice Bob? Bob? Are you there?? Carol Source: Erik Meijer Bob

16 Push versus Pull - I've just finished my report Erik - Something incredible is happening here Alice - I'm sick today Carol Source: Erik Meijer Bob

17 Message-driven Loose coupling No direct dependency: I don t depend on some other responding party No temporal dependency: I m not wasting resources waiting on others Composable Components are assembled in unidirectional chains by integration code, which describes the system wiring No shared state: non-blocking Operation code only generates new messages, it doesn t mutate data (immutability) We don t have multiple threads competing to mutate data: no synchronization needed Any required mutation and synchronization is pushed out of program domain (e.g. database, internals of data structures, etc.)

18 Elastic Scalable systems Scale up or down (adding or removing cores) Minimize shared mutable state, blocking and contention Scale out or in (adding or removing machines) Location transparency, decoupling and resilience Ideal for cloud deployments Resource & cost efficient Pay-per-use

19 Non-blocking Threads of execution competing for a shared resource should not wait by blocking Amdahl s Law: contention is the enemy of scalability

20 Amdahl s Law The theoretical speedup of a program is limited by the part that cannot benefit from the improvement. Source: Wikipedia

Requests/sec JVM server load: sync vs async Raw TCP Rx on Raw TCP async IO, non-blocking Rx Http (RxNettyHttpServer) One thread per connection Thread

21 Requests/sec JVM server load: sync vs async Raw TCP Rx on Raw TCP async IO, non-blocking Rx Http (RxNettyHttpServer) One thread per connection Thread pool (100 threads, servlet) Single thread # concurrent connections Source: Reactive Programming with RxJava, T. Nurkiewicz & Ben Chrisensen, O Reilly

Response time: sync vs async 99 th percentile of response time [ms] (99% requests faster than) One thread per connection Rx on Raw TCP Raw TCP Rx Http async

22 Response time: sync vs async 99 th percentile of response time [ms] (99% requests faster than) One thread per connection Rx on Raw TCP Raw TCP Rx Http async IO, non-blocking Thread pool (fail fast) Single thread # concurrent connections Source: Reactive Programming with RxJava, T. Nurkiewicz & Ben Chrisensen, O Reilly

23 Error rate: sync vs async Request error ratio Single thread Thread pool (fail fast) # concurrent connections One thread per connection Rx on Raw TCP Raw TCP Rx Http async IO, non-blocking Source: Reactive Programming with RxJava, T. Nurkiewicz & Ben Chrisensen, O Reilly

24 Location transparency Components don t depend on being located somewhere to work and find their dependencies Benefits Auto-scaling Load-balancing Take instances offline and replace them while service is running Isolation of failures

25 Resilient Isolation and containment of failures (bulkheads) Failures are messages handled as other events Components dedicated to handle such situations (e.g. supervisor hierarchies in actor systems) Loose coupling Source: Wikipedia (1943)

26 Source: Corellian engineering

27 Source: dzone Bulkheads

28 Circuit breaker calls pass through count fail/success closed trip breaker fail threshold reached trip breaker on attempt failure open calls fail instantly wait for a while attempt call after wait period half-open reset breaker on attempt success

29 Source: Netflix Hystrix Circuit breaker

30 Responsive Modern applications are expected to be responsive Highly adaptive, delightful and rich real-time user interaction Rapid and consistent responsetimes End-user confidence, constant quality of service + +

31 Summary A new paradigm for designing systems in the era of cloud computing Complementary concepts: reactive systems and reactive programming Reactive systems: message-driven, resilient, scalable and responsive Reactive programming: through higher abstraction, we gain explicit time, latency and flow control

Reactive programming: origins & ecosystem. Jonas Chapuis, Ph.D.

Reactive programming: origins & ecosystem Jonas Chapuis, Ph.D. Timeline Functional Reactive Animation (Fran Library, Haskell) Rx 1.0 for.net, Erik Meijer & team at Microsoft Elm language Rx for Java, Netflix